1. Field of the Invention
The present invention relates generally to an ink jet apparatus and a waste liquid absorbing method each of which assures that an image having a high quality can be obtained on a printing medium. More particularly, the present invention relates to an ink jet apparatus for ejecting on the printing medium liquid having a function of insolubilizing a coloring material in ink prior to ejection of the ink.
The present invention is applicable to all kinds of instruments for which a printing medium such as a sheet of paper, unwoven fabric, a sheet of OHP film or the like is used. The applicable instrument is typically exemplified by an office machine and a mass production machine such as a printer, a copying machine, a facsimile or the like.
2. Description of Related Art
An ink jet printing method is utilized for a printer, a copying machine, a facsimile or the like since a low level of noisy sound is generated, the ink jet method is practiced at a low running cost, an apparatus is easily designed with small dimensions, and an image is easily formed by using colored inks.
However, the ink jet printing system has the following specific problems to be solved.
(1) Since a printing operation is performed by ejecting ink droplets from an ink jet head to a sheet of paper, a sheet of OHP film or a similar printing medium, fine ink mist other than the ejected main ink droplets or ink mist ejected to the printing medium rebounds to an ink jet head, causing the ink mist to adhere to an ink ejecting port surface until a large quantity of ink mist get together around the ink ejecting port. In addition, when paper powder or a similar foreign material adheres to the fine mist, ink ejection is obstructed, causing ink droplets to be ejected in an unexpected direction. In an extreme case, ink droplets can not be ejected.
(2) Unless the ink jet head is continuously ejected for a long time inclusive of non-printing time, ink in the nozzle is dried due to vaporization, resulting in the nozzle being clogged with ink having increased viscosity or solidified ink. Thus, there arises a malfunction that ink is ejected in the warped state or no ink ejection is effected.
The ink jet apparatus is generally equipped with recovering means as means for solving the problems as mentioned in the paragraph (1) and the paragraph (2) above. Specifically, when no printing operation is performed, an ink jet head is capped with capping means for the purpose of preventing ink in a nozzle of the ink jet head from being vaporized and dried, resulting in the ink having increased viscosity or adherence to the nozzle. In the case that incorrect ejection is effected due to increased viscosity or adherence, foreign material which cannot be removed by a blade adhere to the ink ejecting port surface, ink having increased viscosity in the nozzle is discharged by operating a suction pump connected to the cap so as to conduct recovering treatment for recovering normal ejection. Here, the discharged ink is sucked in a waste ink absorbing substance disposed in a housing of the apparatus via piping extending downstream of the suction pump.
The capacity of the waste ink absorbing substance is determined depending on the number of times of incorrect printings, the number of times of recovering operations, a quantity of ink squeezed or sucked every recovering operation or a quantity of ink mist discharged from the ink jet head, it is recommendable from the viewpoint of the layout or design of the whole structure of the apparatus that the waste ink absorbing substance is compactly designed to have a small capacity because it is expected that the position where it is to be disposed is not restricted, and moreover, it is fabricated at a low cost. However, if the capacity of the waste ink absorbing substance is set to a quantity originally required by the apparatus, there arises an inconvenience of maintenance that the waste ink absorbing substance must be periodically replaced with a new one. On the contrary, when a waste ink absorbing substance having a required capacity is disposed on the apparatus, the waste ink absorbing substance is relatively enlarged, causing it to be fabricated at an increased cost, and moreover, the housing of the apparatus is enlarged in size. In this connection, a technology for minimizing a volume of the waste ink absorbing substance by utilizing vaporization of ink is disclosed on an official gazette of Japanese Patent Application Laid-Open No. 22065/1982.
On the other hand, in the case that an image has insufficient water resistibility or a color image is formed on a printing medium that is called a plain paper with the aforementioned apparatus having an ink jet printing method applied thereto, a request for an image having a high density without an occurrence of feathering and a request for an image having no oozing of coloring substance among colors cannot exist together, resulting in a quality of colored image being remarkably degraded.
In recent years, as a method of improving water resistibility of an image, ink containing a coloring material having resistibility against water has been put in practical use. However, since this ink still has an insufficient water resistibility, and it is ink which is theoretically hardly soluble in water after drying, it has a drawback that ink is liable to cause a failure of ink ejection.
In view of the foregoing fact, Japanese Patent Application Laid-Open No. 63185/1989 discloses the technology in which transparent or translucent treatment liquid containing a coloring substance which is insoluble in a solvent is caused to adhere to a printing medium with the aid of an ink jet head directly before a printing operation is performed. However, with respect to this technology, the problem specific to the ink jet apparatus is also arises to a head for ejecting the treatment liquid, and when the treatment liquid is not ejected from the nozzle as a result of failure of ejection, it occurs sometimes that the water resistibility and quality of the portion of images which is affected by the failure of ejection of the treatment liquid are remarkably degraded. For this reason, it is necessary that the head for the treatment liquid is equipped with recovering means similar to that used in the ink jet head.
FIG. 1 schematically shows by way of example the structure of a conventional ink jet apparatus which is equipped not only with recovering means for recovering an ink jet head but also with recovering means for recovering a head for ejecting treatment liquid. Here, each of a plurality of ink jet cartridges 1 includes an ink tank portion. A plurality of ink jet cartridges 1, each containing treatment liquid for insolubilizing coloring ink and coloring material for printing, are mounted on a carriage 3 at predetermined positions. The carriage 3 is slidably supported on a shaft 4 extending in the main scanning direction, and a driving belt 5 serves to transmit the driving force of a driving motor 6 for reciprocatingly displacing the carriage 3 along the axis of the shaft 4. A printing medium 11 is conveyed while its printing surface is flatly restricted by a platen 12. At this time, ink jet head portions 2 of the ink jet cartridges 1 mounted on the carriage 3 is projected downward of the carriage 3 to assume a position between two sets of conveying rollers (not shown) of the printing medium 11, and ink ejecting port forming surfaces of the ink jet head portions 2 faces to the printing medium 11 which is located in parallel thereto while comes in pressure contact with the guide surface of the platen 12.
In addition, a recovering system unit 20 is arranged on the home position side located on the right-hand side in FIG. 1. The recovering system unit 20 has a plurality of cap units 21 corresponding to the respective ink jet head portions 2 of a plurality of ink jet cartridges 1. The cap units 21 can be raised and lowered in the vertical direction. When the carriage 3 is located at the home position, it is connected to the ink jet head portions 2 so as to cap the latter therewith to prevent an occurrence of incorrect ejection due to increased viscosity or chemical fixing induced by evaporation (vaporization) of ink in the ink ejection port. A pump unit (not shown) is disposed in the recovering system unit 20. This pump unit serves to generate negative pressure when suction recovering treatment is conducted by connecting the cap unit 21 to the ink jet head portions 2. As the suction recovering treatment is conducted, the ink and the treatment liquid sucked from the ink jet head is absorbed in a waste liquid absorbing substance 23 via a tube 22 by driving the pump unit.
When suction recovering treatment is conducted with the ink jet apparatus as mentioned above, two kinds of materials, i.e., the treatment liquid and ink are present in the waste liquid absorbed in the waste liquid absorbing substance 23. However, although these two kinds of waste liquids are fluid per se, they will have an increased viscosity when they are mixed with each other. Thus, there arise the following problems.
(1) When both liquids are absorbed in a waste liquid absorbing substance, they contact with each other to form a waste mixed liquid, whose viscosity increases, so that the mixed liquid accumulates on the waste liquid absorbing substance. Therefore, it is difficult for the waste liquid absorbing substance to absorb the waste mixed liquid fully.
(2) If the height of the space for storing the waste ink is to be enlarged taking into consideration accumulation of the insolubilized waste mixed liquid, the entire height of the ink jet apparatus becomes too high to be practically acceptable
(3) A possible countermeasure for avoiding the accumulation of would be to provide two separate recovering systems one for recovering the treatment liquid and the other for ink, and also provide waste liquid absorbing substances separately for ink and treatment liquid so as to avoid increased viscosity of the waste liquid. However, this solution is accompanied by a considerable increase in cost and by enlargement in size of the ink jet apparatus.